Capsular polysaccharides of serogroups A, B, C, Y and W-135 are major virulence factors of the important human pathogen Neisseria meningitidis. Despite the essential role of capsule in meningococcal disease, the genetic basis for expression of meningococcal capsules is not fully defined. In this continuation application, we propose to determine the pathways regulating meningococcal capsular polysaccharide assembly and transport to the cell surface. In Specific Aim 1, we will define the genetic basis for formation of the meningococcal capsule polymer. New genes to be studied include the unique genes sacA-D of the serogroup A capsule biosynthesis locus, and two genes, kpsF and pglB2, located outside the capsule locus, that when mutated reduce meningococcal capsule expression in all serogroups and increase sensitivity to killing by human sera. Preliminary data indicate that kpsF- and pglB2-encoded proteins influence Kdo and undecaprenol phosphate production and that these intermediates are required for capsule polymer assembly. In Specific Aim 2, the genetic and biochemical basis for the novel lipid modifications (1,2 diacylglycerol C16:0 or C18:0) of meningococcal capsule polymers will be determined and the role of lipA and lipB in lipidation of the capsule polymer, capsule assembly, transport and function will be defined. In Specific Aim 3, the function of the ctrA, ctrB, ctrC and ctrD capsule transport operon genes and their encoded proteins will be determined. Very limited information is available regarding the mechanisms of meningococcal capsule translocation across the two cellular membranes and about the recognition and interaction between the transport apparatus and the assembled capsule polymers. The proposed studies have direct application to the development of new meningococcal vaccine strategies. CtrA, for example, is a surface-exposed protein, appears conserved, is essential for capsule expression and is a candidate for conjugate or other meningococcal vaccines that prevent disease due to all invasive serogroups. Antibiotic resistance is also increasing in meningococci. These studies also can identify novel pathways that interfere with meningococcal capsule expression, which, when blocked, would increase meningococcal susceptibility to killing by host defenses and decrease meningococcal transmission to new human hosts.